WASHINGTON, Feb 23 (Reuters) - U.S. Secretary of State John Kerry on Sunday condemned last week's attacks in Nigeria by the Islamist group Boko Haram and underscored a commitment to help Nigerian authorities crack down on the militants the United States deems a terrorist organization.

"Unspeakable violence and acts of terror like the ones committed by Boko Haram last week in northern Nigeria are horrific, wrong and have no place in our world," Kerry said in a statement.

Boko Haram gunmen killed about 100 people in the northeastern Nigeria town of Bama on Wednesday, storming the town, firing on a school, shooting or burning to death dozens of people and trashing the palace of a traditional ruler of one of West Africa's oldest Islamic kingdoms.

Last Sunday, Boko Haram gunmen killed more than 100 people in the village of Igze, spraying homes with bullets, detonating explosions and burning down dozens of houses.

"We support Nigerian authorities' efforts to investigate these cowardly acts and to bring the perpetrators to justice," Kerry added.

Boko Haram and other splinter Islamist groups are seen as the biggest security threat in Nigeria, Africa's most populous country and top oil exporter.

"The people of northern Nigeria deserve to live free from violence and from terror," Kerry said. "That's why the United States is providing counterterrorism assistance to help Nigerian authorities develop a comprehensive approach to combat the threat posed by Boko Haram while protecting civilians and ensuring respect for human rights."

Nigerian President Goodluck Jonathan ordered extra troops into northeast Nigeria in May to crush Boko Haram, which wants to create a breakaway Islamic state in the largely Muslim north. The offensive, backed by air power, has so far failed.

Kerry said the United States remains "a committed partner" of Nigeria's government as it targets Boko Haram and associated groups.

The United States last November designated Boko Haram and another Nigerian Islamist group, Ansaru, as foreign terrorist organizations, making it a crime to provide them with material support.

The White House directed U.S. agencies to block financial transactions with the two groups, which it blamed for thousands of deaths in northeast and central Nigeria, including attacks on churches and mosques and a 2011 suicide bombing of the United Nations building in Abuja.

The militants have retreated into the remote, hilly Gwoza area bordering Cameroon, from where they mount deadly attacks against civilians they accuse of being pro-government, and are abducting scores of girls - a new tactic eerily reminiscent of Uganda's cult-like Lord's Resistance Army in decades past. (Reporting by Will Dunham; Editing by Marguerita Choy)